This patch corrects the retrieval of the equality function when it is
inherited from a parent tagged type.

2018-11-14  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* exp_ch4.adb (Expand_N_Op_Eq): Remove duplicated code and use
	routine Find_Equality instead.
	(Find_Equality): New routine.

gcc/testsuite/

	* gnat.dg/equal4.adb, gnat.dg/equal4.ads,
	gnat.dg/equal4_controlled_filter.ads,
	gnat.dg/equal4_full_selector_filter.ads,
	gnat.dg/equal4_smart_pointers.ads: New testcase.

From-SVN: r266114